How do muscle strains actually happen in sport?

Muscle strains remain one of the most stubborn problems in sport. They are common in recreational, trained, and elite athletes, and in many sports they are among the leading causes of missed training and competition. What makes them especially frustrating for clinicians is that, despite decades of prevention work, injury rates have not fallen as much as hoped.

A recent systematic review tackled this question by examining video-recorded muscle injuries in sport. The review included 21 studies and 728 indirect and non-contact muscle injuries captured across a range of sports, although football dominated the dataset. The researchers focused on the situational characteristics of injury: whether there was contact, what movement the athlete was performing, the position of the joints at the assumed injury moment, and whether the injury happened during running, kicking, changing direction, or another sport-specific action.

One of the clearest findings was that most muscle injuries were truly non-contact. About three-quarters occurred without any direct or indirect collision. This reinforces the idea that many muscle strains are not random accidents or the result of being hit, but arise from the athlete’s own movement demands. In many cases, the injury occurred while the muscle-tendon unit was lengthening under active contraction. In practical terms, the athlete was trying to produce force, decelerate, or control a rapid movement while the muscle was being stretched. This eccentric-like demand appears to be a common thread across many muscle groups.

Running was the most common injury-inciting activity overall. Nearly half of non-contact injuries were associated with running, sprinting, or acceleration-type actions. However, the review also showed that running is not the whole story. Many injuries happened during sport-specific manoeuvres such as kicking, reaching, lunging, or changing direction. These are not just background details. They tell us that muscle injuries are often tied to precise tasks that combine speed, lengthening, and force production in distinct ways. That has major implications for prevention. It is not enough to strengthen a muscle in isolation; the athlete must be prepared for the specific movement situations in which injuries actually occur.

Hamstring injuries were the most extensively studied, and they showed a fairly consistent pattern. Most were non-contact and frequently running-related. The classic picture was an athlete moving with the knee close to extension while the hip was flexed, especially during high-speed running, sprinting, or acceleration. The knee was usually moving toward extension at the assumed injury moment, while hip motion varied more. This fits with long-standing theories that hamstring injuries often occur when the muscle is under high load at long length. Yet the review also highlighted that not all hamstring injuries happen in the same way. Some occurred during lunging or decelerating actions, and others during kicking or reaching. This reminds therapists that hamstring strain is not a single mechanism injury. Sprint-related hamstring injury is common, but closed-chain deceleration patterns and stretch-type injuries also deserve attention.

Adductor injuries showed a different profile. These injuries often occurred during kicking, reaching, or change-of-direction actions. The common kinematic theme was rapid lengthening of the adductor muscle-tendon unit through hip extension, abduction, and external rotation, often while the athlete was still actively trying to control or produce movement. In other words, the adductors were not simply being stretched passively; they were under load while being lengthened. For therapists, this supports the clinical impression that adductor injuries are closely tied to multiplanar control, especially in sports such as football, hockey, and basketball where athletes frequently cut, reach, and kick from wide hip positions.

Rectus femoris and quadriceps injuries showed yet another distinct pattern. These injuries were much less often running-related and far more often associated with kicking. The typical movement involved a flexing hip and an extending knee, a combination that strongly loads the biarticular rectus femoris. This makes sense biomechanically. During the kicking motion, rectus femoris has to manage simultaneous hip and knee demands, especially during the transition from the backswing to the forward swing. For therapists, this finding reinforces the need to train not only quadriceps strength, but also timing, velocity tolerance, and sport-specific kicking mechanics.

Calf injuries, especially gastrocnemius injuries, were most often linked to running and push-off type actions. The typical injury situation involved ankle dorsiflexion with the knee close to extension. In the limited detailed case analyses available, the ankle was often already in more than 10 degrees of dorsiflexion while the knee remained nearly straight. This is a mechanically demanding position for the gastrocnemius, which crosses both the knee and ankle. The pattern resembles the vulnerable position often discussed in Achilles tendon injury, suggesting that the calf muscle-tendon complex faces high stress when lengthened across both joints during rapid propulsion or stepping back.

Although the review identified clear differences across muscle groups, it also revealed important similarities. Many of these injuries involved biarticular muscles. Many occurred during high-speed actions. Many happened when the muscle was highly active while lengthening. These shared features suggest that there are broad principles of muscle injury causation, even though each muscle group expresses them differently depending on anatomy and sporting task. Hamstrings and calves were more strongly associated with running. Adductors and rectus femoris were more often associated with kicking, reaching, or change-of-direction tasks. This means prevention should combine two levels of thinking: general principles of load tolerance and eccentric control, and muscle-specific, sport-specific rehearsal of vulnerable positions.

An interesting secondary finding concerned the timing of injuries during matches. Across the limited data available, there was a slight tendency for more injuries to occur in the first half than in the second. This challenges the common assumption that fatigue late in the game is always the dominant driver. It suggests that inadequate preparation for early high-intensity actions, insufficient warm-up, or beginning play with unresolved symptoms may be just as important as end-of-match fatigue. That said, the evidence here remains limited, and the authors rightly caution against overinterpreting this point.

The review also supports a more precise approach to prevention. Hamstring and calf injury prevention should likely include not only eccentric strengthening but also sprint exposure, acceleration and deceleration work, and preparation for reaching or kicking tasks when relevant. Adductor prevention should involve training in hip abduction, extension, and external rotation under load, rather than focusing only on isolated squeeze strength. Rectus femoris prevention should consider the demands of kicking mechanics and rapid hip-knee coordination. More broadly, prevention should reflect the true movement ecology of the sport. The idea that “the problem is the solution” has merit here: if injuries occur in specific situations, athletes need controlled exposure to those situations in training.

This review has limitations. Most included studies focused on male football players, so the findings may not apply equally across sports, levels, and female athletes. Video analysis also tends to capture more obvious acute injuries and may miss overuse-type presentations.